Field of the Invention
The present invention relates generally to disk drives for portable and desk top computers. More particularly, it relates to a power management method for hard disk drives used in such computers that optimizes around each user.
Portable computers using battery power are becoming increasingly popular and are evolving rapidly. As more and more efficient logic and displays become available, the dominant factor in determining battery life is the hard disk drive. If hard disk drives are not able to improve their efficiency, the computer users of the future will seek other forms of mass storage to achieve acceptable levels of battery life. Thus, improvement in the energy efficiency of hard disks drives will be critical to their ability to continue as the low cost storage device of choice.
One approach to reducing hard disk power consumption is to work on improving the efficiency of the electro-mechanical apparatus of the drive. A second approach to improving hard disk power consumption is to attack the method in which the hard disk drive is used.
Some work has been done on the second approach, but it is limited in scope and is totally controlled by the host processor.
The work previously done starts with ANSI ATA. This group has defined four power states that a drive may occupy. These states are:
Sleep: This is the lowest power consumption state. The drive requires a reset to be activated and the time to respond to an access command from this state could be 30 seconds or more. This implies that the disk is spun down, the heads are unloaded or out of the data zone, the internal drive processor is turned off, and all of the interface logic is turned off except the reset recognition logic.
Stand By: In this state, the drive is capable of accepting commands, but the media is not immediately accessible. It could take as long as 30 seconds or more to respond to an access command from this state. This implies that the disk is spun down and the heads parked but the internal processor and interface are still active.
Idle: In this state, the drive is capable of responding immediately to media access requests but may take longer to complete the execution of a command because it may be necessary to activate some circuitry. This implies the disk is spinning, the internal processor and interface electronics are active, but the servo system controlling the head position or some other circuitry may be inactive.
Active: The active state is the normal operating state of a disk drive from which it responds to all access requests in the minimum time of which it is capable. This implies that the disk is spinning, the heads are actively being controlled by the servo system and all circuitry is active.
To date, ANSI ATA has developed interface standards that define commands that allow the host computer to place the disk drive into the power states previously defined, or to set timers for determining when the drives should switch states automatically.
U.S. Pat. No. 4,933,785, issued to Morehouse, et al, describes power saving states which are equivalent to the ANSI ATA idle and stand by states and describes using the states with fixed wait times either as a default or host defined. The Morehouse patent teaches switching the drive to the lower power state after a predetermined and fixed wait time. Wait time is defined as the time after the finishing of the last access request before the drive is switched to a lower power state. In practice, after finishing an access to the disk drive, the host would start a wait time counter. If access to the disk drive is needed during the defined wait time, the access request is executed and the wait time clock is reset to zero and restarted. If a request is not received before the wait time counter times out, the drive switches to the lower power state. Any requests received thereafter are responded to from the lower power state. However, Morehouse does not define any criteria or method for determining how long the wait time should be.